1. Field
This application relates generally to wireless communication and more specifically, but not exclusively, to selecting a modulation and coding scheme for beamformed communication.
2. Introduction
Some wireless communication apparatuses (e.g., devices) employ directional antenna systems to improve antenna gain. To provide this directionality, the signals that drive the different antennas of the antenna system are weighted differently (e.g., in terms of signal phase and, optionally, amplitude).
IEEE 802.11ad is directed to wireless communication in the 60 GHz frequency range. Due to the high propagation losses at these frequencies, directional antenna systems are supported by this standard to improve antenna gain and thereby improve communication performance. Specifically, the antennas for each 802.1 lad apparatus may be configured to support a quasi-omni-directional beam pattern, a sector level beam pattern, or a refined beam pattern (i.e., a narrower beam than a sector level beam). To provide these different beam patterns, an appropriate antenna weight taken from a set of antenna weights (e.g., a set comprising: {1, −1, j, −j}) is assigned to each antenna. For the case of the set {1, −1, j, −j}, for a given antenna, the amplitude is always “1” and the phase is one of 0°, 90°, 180°, and 270°.
For a given beam pattern, an apparatus may support several modulation and coding schemes (MCSs) each of which specifies a particular transmission rate. A conventional rate selection algorithm will periodically conduct goodput calculations to determine whether the apparatus should move up to the next highest defined rate or move down to the next lowest defined rate. However, these algorithms are based on an assumption that changes in MCS (e.g., based on the measured signal quality) will occur relatively slowly.